In the field of mobile communication systems mainly including portable telephone systems, the number of users increases rapidly, and also diversified content services have increased the amount of transmission data. This escalates demands for higher communication qualities. However, since the radio wave resources for communication have limitation, for example, in the case of communication congestion in a portable telephone system, namely, when a congestion condition occurs at a base transceiver station, problems occurs in communication quality, such as partial interruption of communication.
As countermeasures, various methods have been adopted. One of them can eliminate the congestion condition by flow control of communication data in a base transceiver station transmitting-receiving control system. This method is adopted for flow control of individual data concerned with common channels particularly in the case that common channels for multiplex transmission of data and individual channels are included as radio wave transmission lines between a base transceiver station and mobile terminals, providing accomplishments in acquiring the required communication quality.
Hereinbelow, a conventional method of flow control for the common channel in a base transceiver station will be described.
FIG. 1 shows a construction of a base station transmitting-receiving control apparatus in wireless communication providing multiple access including common channels for multiplex transmission. Here, it shows a data flow from TCP/IP (transmission control protocol/Internet protocol) network 2 to the base transceiver station (BTS; base transceiver station) 4 around base station transmitting-receiving control apparatus 1 for wireless communication, with assumption of multiple access including common channels for multiplex transmission.
Data for each session is transmitted from TCP/IP network 2 to exchange 3 and from exchange 3 via a plurality of individual lines L to transmitting-receiving control apparatus 1 of the base transceiver station. The data is subjected to necessary processes in transmitting-receiving control apparatus 1 and then transmitted to base transceiver station 4. Further, while not shown in the drawing, the multiplexed data is transmitted via the base transceiver station to communication terminals (remote terminals), which are communication objects.
Transmitting-receiving control apparatus 1 comprises individual trunk apparatus 11 receiving individual lines L, common buffer apparatuses 12a, 12b corresponding to common channels, multiplexing apparatus 13 providing connection to base transceiver station 4 with multiplexing a plurality of channels. Within individual trunk apparatus 11, for each individual line L, individual line unit “a” for receiving individual data is provided for each session. In the following description, it is assumed that there are n channels including channel 1 (ch.1) and channel 2 (ch.2) for common channels and the remaining channels are for individual channels, and that common buffer apparatus 12a corresponds to channel 1 which temporarily stores individual data pieces (a1, a2, a3) from the individual line unit for three lines. Similarly, the common buffer apparatus 12b corresponds to channel 2 that temporarily stores individual data pieces (a4, a5, a6) from the individual line unit for three lines. Further, individual channels in multiplexing apparatus 13 correspond to individual line unit “a” in the individual trunk apparatus 11 one to one, respectively.
Next, the operation and process in transmitting-receiving control apparatus 1 will be described.
At first, individual trunk apparatus 11 receives individual data for each session with the individual line unit “a” and transmits to common buffer apparatus 12a the individual data piece (for example, individual data pieces a1, a2, a3) requiring the multiplexing process. Individual trunk apparatus 11 transmits individual data corresponding to an individual channel to multiplexing apparatus 13 as it is.
Common buffer apparatus 12a temporarily stores these pieces of data transmitted from individual trunk apparatus 11 and then transmits them to multiplexing apparatus 13. Multiplexing apparatus 13 executes a multiplexing process for the data received from common buffer apparatus 12a and transmits it to base transceiver station 4 as data of common channel (ch.1).
Now, the method of flow control will be described for the case that a congestion condition occurs in common channel ch.1. on the basis of FIG. 2 in which only individual data pieces of sessions associated with the common channel ch.1 are shown for individual trunk apparatus 11.
At first, in S400, individual data for each session is transmitted from individual trunk apparatus 11 to common buffer apparatus 12a. As a result, an amount of data temporarily stored in common buffer apparatus 12a, namely, an amount of the used portion in the buffer, exceeds a congestion threshold value in step S401. That is, a congestion condition is detected.
As a result, in step S402, common buffer apparatus 12a informs individual trunk apparatus 11 about setting the flow control for individual data pieces a1, a2, and a3 using a broadcast message. In response to this notice of setting the flow control, the individual trunk apparatus 11 uniformly stops or restricts transmission of individual data pieces a1, a2, and a3 to common buffer apparatus 12a. 
Stopping or restricting the transmission causes the amount of the used portion of the buffer to decrease below the congestion threshold in step S403, eliminating the congestion condition in common channel ch.1. In response to this, in step S404, common buffer apparatus 12a informs individual trunk apparatus 11 about release of the flow control for individual data pieces a1, a2, and a3. Then, in step S405, transmission from individual trunk apparatus 11 to common buffer apparatus 12a is restored to the usual data flow rate. Here, the data flow rate is represented as an amount of data per a unit interval, typically, the number of bits of data per a unit interval.
According to the above-described method the congestion condition can be eliminated in common channel ch.1. However, in this method of flow control, because the data rate is uniformly restricted for each session, the required communication quality or performance may not be achieved due to data delay in accordance with the quality of service (QoS; Quality of service) class required for each session. For example, though no problem occurs in communication of a still picture by such a flow control, in a moving picture communication associated with a voice, the required QoS may not be maintained because a portion of voice or a picture may drop out.